Japanese Unexamined Patent Application Publication No. 2006-174588 (hereinafter referred to as Patent Document 1) describes a technology in this field. This publication describes a lens unit including an actuator. The actuator includes a fixed plate that is fixed to a lens barrel, a movable frame that retains an image shake correction lens, and steel balls that support the movable frame. In the actuator having such a structure, the movable frame is moved with respect to the fixed plate. Accordingly, the image shake correction lens is moved in a direction orthogonal to the optical axis, so that blurring of an image formed on a film surface can be suppressed.
The movable frame included in the actuator described in Patent Document 1 has three degrees of freedom, which include two degrees of freedom for translation and one degree of freedom for rotation. The movable frame is movable along a two-dimensional plane, and is rotatable around a desired position. However, the movable frame can be moved to a desired position on the fixed plate as long as the movable frame has two degrees of freedom. When the movable frame has the above-described degrees of freedom, there is a risk that the movable frame will be moved or rotated in an unintended direction. Therefore, the actuator described in Patent Document 1 has a problem in that accuracy of the image shake correction may be reduced owing to the movement or rotation of the movable frame in the unintended direction.